1. Field of the Invention
The present invention relates to an apparatus for fabricating a semiconductor device, and more particularly, to an apparatus for fabricating a semiconductor device using a 4-way valve with improved purge efficiency by improving a valve system for gas supplied to a reaction chamber, a method of controlling the 4-way valve, and a method of fabricating a semiconductor device using the apparatus.
2. Description of the Related Art
Semiconductor devices are fabricated by repeatedly performing processes such as deposition and patterning of a thin layer on a surface of a substrate, i.e., a wafer. Deposition and patterning of a thin layer is usually performed in a semiconductor process module. A semiconductor process module has a configuration that differs depending on a process to be performed in fabrication of a semiconductor device, but it fundamentally includes a reaction chamber defining a reaction area in which a wafer is loaded and hermetically sealed and a valve system which supplies a gas material to the reaction chamber.
Chemical vapor deposition (CVD) or atomic layer deposition (ALD) are usually used to deposit a thin film on a wafer through a chemical reaction of a gas material. Unlike physical deposition using sputtering, CVD and ALD are similar to each other in that they use chemical reaction between two or more gas materials. However, in CVD, multiple gas materials are simultaneously supplied to a reaction area in a reaction chamber including a wafer so that a reaction product is deposited onto a surface of the wafer from above. In contrast, in ALD, multiple gas materials are sequentially supplied to the reaction area in the reaction chamber so that chemical reaction between the gas materials is limited to only the surface of the wafer.
Despite a disadvantage that the ALD is slow in deposition since the chemical reaction is limited to only the surface of a wafer, ALD is essential to fabrication of a dielectric layer, a diffusion preventing layer, a gate dielectric layer, etc., for a memory capacitor that requires a high-purity and high-uniformity thin film. ALD is advantageous in that deposition and thickness of a thin film whose thickness is decreased with the micronization of a semiconductor device can be controlled precisely.
Due to the characteristics of the ALD, a purge process of removing gas remaining in a reaction chamber before and after a gas material is supplied to the reaction chamber when gas materials are sequentially supplied is mandatory.
FIG. 1 is a schematic diagram illustrating a gas valve system of a conventional ALD apparatus in which ALD is performed. FIG. 2 is an enlarged view of a part of the gas valve system in which dead volume (DV) occurs. FIG. 3 is a cross sectional view of the part shown in FIG. 2, taken along the line AA′, in which a 2-way valve is closed. FIG. 4 is a cross sectional view of the part shown in FIG. 2, taken along the line AA′, in which the 2-way valve is open.
The conventional ALD apparatus and ALD using the same will be described briefly with reference to FIGS. 1 through 4.
Referring to FIG. 1, a source gas supply source 22, a reactive gas supply source 24, a purge gas supply source 28, a first carrier gas supply source 26, and a second carrier gas supply source 30 supply a source gas S1, a reactive gas S2, a purge gas P2, and carrier gases P1 and P3, e.g., argon gases, respectively, to a reaction chamber 10 via a source gas supply pipe 22a, a reactive gas supply pipe 24a, a purge gas supply pipe 28a, a first carrier gas supply pipe 26a, and a second carrier gas supply pipe 30a, respectively.
A discharge pump 12 is installed at the back of the reaction chamber 10 to control the inner pressure of the reaction chamber 10. A throttle valve 14 is installed between the reaction chamber 10 and the discharge pump 12 to maintain the inner pressure of the reaction chamber 10 constant.
In a source gas supply line, the first carrier gas supply pipe 26a is connected to and extended from the first carrier gas supply source 26 to supply the carrier gas P1. The source gas supply source 22 is connected in parallel through first and second 3-way valves 32 and 34. An on/off valve, i.e., a first 2-way gate valve 42 is installed between the first and second 3-way valves 32 and 34. A bypass 16 is connected to the first carrier gas supply pipe 26a in the back of the second 3-way valve 34 through a third 3-way valve 36. An end of the bypass 16 is connected between the throttle valve 14 and the discharge pump 12 on a discharge pipe 13. An end of the first carrier gas supply pipe 26a is connected to the purge gas supply pipe 28a through a fourth 3-way valve 38.
In a purge gas supply line, the purge gas P2 is supplied from the purge gas supply source 28 to the reaction chamber 10 through the purge gas supply pipe 28a. The fourth 3-way valve 38 is installed at a junction of the purge gas supply pipe 28a and the first carrier gas supply pipe 26a. A second gate valve 44 is installed between the purge gas supply source 28 and the fourth 3-way valve 38.
In a reactive gas supply line, the carrier gas P3 is supplied from the second carrier gas supply source 30 to the reaction chamber 10 through the second carrier gas supply pipe 30a and the reactive gas S2 is supplied from the reactive gas supply source 24 to the reaction chamber 10 through the reactive gas supply pipe 24a and the second carrier gas supply pipe 30a to which the reactive gas supply pipe 24a is connected. A third gate valve 46 is installed between the reaction chamber 10 and the junction of the reactive gas supply pipe 24a and the second carrier gas supply pipe 30a. A fourth gate valve 48 is installed between the junction and the reactive gas supply source 24.
The open/closed state of the inlet and outlet of the third and fourth 3-way valves 36 and 38 will be described with reference to FIGS. 2 through 4. Unlike FIGS. 2 through 4, FIG. 1 just functionally illustrates the inlet and outlet of the third and fourth 3-way valves 36 and 38 according to a flow direction of supplied gas.
The third and fourth 3-way valves 36 and 38 are diaphragm valves. A flow of a gas material according to on/off of the third 3-way valve 36 will be described. The third 3-way valve 36 installed at the junction of the first carrier gas supply pipe 26a and the bypass 16 includes a first vertical via hole 36h1, which is vertically connected to the first carrier gas supply pipe 26a penetrating straight through a body 36c, and a second vertical via hole 36h2 which is vertically connected to an end of the bypass 16. A diaphragm 36e moved up and down by a pressure is installed above a surface of the body 36c through which the first and second vertical via holes 36h1 and 36h2 are exposed within a housing 36d to define a predetermined space.
When the third 3-way valve 36 is turned off, that is, when the diaphragm 36e moves downward and closely contacts the surface of the body 36c to close the first and second vertical via holes 36h1 and 36h2, as shown in FIG. 3, the first carrier gas supply pipe 26a is open and enables the first carrier gas P1 or the source gas S2 to flow to the fourth 3-way valve 38, but a gas flow to the bypass 16 is blocked.
When the third 3-way valve 36 is turned on, that is, when the diaphragm 36e moves upward and is separated from the surface of the body 36c to open the first and second vertical via holes 36h1 and 36h2, as shown in FIG. 4, the first carrier gas supply pipe 26a is open and enables the first carrier gas P1 or the source gas S2 to flow to the fourth 3-way valve 38, and simultaneously, a gas material flowing out through the first vertical via hole 36h1 passes through a space between the surface of the body 36c and the diaphragm 36e and flows into the bypass 16 through the second vertical via hole 36h2.
Referring to FIGS. 1 through 4, regardless of the on/off state of the third 3-way valve 36, a second outlet 36b of the third 3-way valve 36 is open. Accordingly, whether the first carrier gas P1 or the source gas S1 is supplied to the reaction chamber 10 through the third and fourth 3-way valves 36 and 38 depends on whether an inlet 38b of the fourth 3-way valve 38 is open or closed. As a result, when the inlet 38b of the fourth 3-way valve 38 is closed, the first carrier gas P1 or the source gas S1 does not flow to the fourth 3-way valve 38 but flows into the bypass 16 even when the second outlet 36b of the third 3-way valve 36 is open.
A process of depositing a reaction product S1+S2 to form a thin film on a surface of a substrate using ALD using the source gas S1 and the reactive gas S2 will be described below.
In a source gas pulsing stage, the source gas S1 is supplied to the reaction chamber 10 loaded with a wafer, i.e., the substrate (not shown) so that a source gas material is attached to a surface of the substrate. Here, the first gate valve 42 is turned off to be closed; a first outlet 32a of the first 3-way valve 32 is open; an inlet 34a and an outlet 34b of the second 3-way valve 34 are open; a first outlet 36a of the third 3-way valve 36 toward the bypass 16 is closed; the second outlet 36b of the third 3-way valve 36 is open; and the inlet 38b and an outlet 38a of the fourth 3-way valve 38 are open. Accordingly, the source gas S1 is supplied to the reaction chamber 10 together with the first carrier gas P1. Meanwhile, the purge gas P2 is continuously supplied to the reaction chamber 10 and the second carrier gas P3 is also supplied to the reaction chamber 10 in a state where the fourth gate valve 48 is closed. Generally, in a 3-way valve, when one flow path is closed, another flow path is open.
Thereafter, in a source gas purging stage, source gas residues that are not attached to the surface of the substrate are removed from the reaction chamber 10. Here, the first gate valve 42 is open; the first outlet 32a of the first 3-way valve 32 is closed (when a second outlet 32b of the first 3-way valve 32 is open according to the characteristic of a 3-way valve); the inlet 34a of the second 3-way valve 34 is closed (when the outlet 34b of the second 3-way valve 34 is open); the first outlet 36a of the third 3-way valve 36 toward the bypass 16 is open (when a second outlet 36b of the third 3-way valve 36 is open); and the inlet 38b of the fourth 3-way valve 38 is closed (when the outlet 38a of the fourth 3-way valve 38 is open). Accordingly, the residues of the source gas S1 within the supply pipes flow to the bypass 16 together with the first carrier gas P1 and the residues of the source gas S1 within the reaction chamber 10 purged by the purge gas P2 continuously supplied to the reaction chamber 10. Here, the second carrier gas P3 is also supplied to the reaction chamber 10 in a state where the fourth gate valve 48 is closed.
Subsequently, in a reactive gas pulsing stage, the reactive gas S2 is supplied into the reaction chamber 10 in a state where the source gas S1 has been deposited on the surface of the substrate so that the source gas S1 reacts with part of the reactive gas S2, thereby forming a reaction product on the surface of the substrate. Here, a supply line for the first carrier gas P1 and the purge gas P2 is the same as that in the source gas purging stage, with the exception that the fourth gate valve 48 is open so that the reactive gas S2 is supplied into the reaction chamber 10 together with the second carrier gas P3. Meanwhile, the purge gas P2 is continuously supplied into the reaction chamber 10.
Subsequently, in a reactive gas purging stage, the residues of the reactive gas S2 other than the reaction product of the source gas S1 and the reactive gas S2 deposited on the surface of the substrate are removed from the reaction chamber 10. Here, a supply line for the first carrier gas P1 and the purge gas P2 is the same as that in the source gas purging stage. The fourth gate valve 48 is closed and only the second carrier gas P3 is supplied to the reaction chamber 10.
As described above, when one cycle of the source gas pulsing stage, the source gas purging stage, the reactive gas pulsing stage, and the reactive gas purging stage is performed, the reaction product of the source gas S1 and the reactive gas S2 is deposited to be very thin on the surface of the substrate. Several or several thousands of cycles may be performed to form a desired thin layer on the surface of the substrate.
However, the conventional ALD apparatus has a problem in that dead volume (DV), in which purging is not performed and a source gas material is stagnant between valves, occurs. In FIG. 2, a hatched portion between the third 3-way valve 36 and the fourth 3-way valve 38 corresponds to a DV portion. In detail, when source gas purging starts after source gas pulsing in which the source gas S1 is supplied to the reaction chamber 10 through the third 3-way valve 36 and the fourth 3-way valve 38, as described above, supply of the source gas S1 is interrupted and the first carrier gas P1 is discharged through the bypass 16. Here, the source gas S1 remains in the portion of the first carrier gas supply pipe 26a corresponding to the DV portion between the third 3-way valve 36 and the fourth 3-way valve 38. The remaining source gas is still stagnant in the first carrier gas supply pipe 26a during the succeeding reactive gas pulsing and purging stages. Only after a single ALD cycle is completed, the remaining source gas in the DV portion flows into the reaction chamber 10 when the outlet 38b of the fourth 3-way valve 38 is open in the source gas pulsing stage in a subsequent cycle.
When a gas material such as a source gas is stagnant in a DV portion for a long time, degradation occurs and an additional dummy process of removing the remaining source gas is required. In particular, when a dielectric layer or a complex layer, which includes multiple layers made of different materials, is formed using the conventional ALD apparatus, different source gas materials may react with each other in the DV portion, thereby generating unnecessary particles. As a result, a thin film formed through the ALD may have defects or low uniformity.
The source gas material remaining in the DV portion may be slowly diffused and discharged, but it is not completely removed even after several minutes. Taking into account that an ALD cycle takes several seconds, it is very difficult to perform ALD using different kinds of source gas without purging and removing the source gas remaining in the DV portion.